The present invention. relates generally to a method for decontamination of surfaces. More particularly, the present invention relates to using an aqueous solution having particular compositions to remove radioactive contaminants from a given area, location or surface.
Contamination of various areas or surfaces from radioactive or other unwanted materials is a common problem. The contamination of an area or surface may occur as a result of contact with a radioactive isotope during transport, storage, use in a nuclear reactor, mining operations, or a variety of other industrial, medical, or military activities. Current Nuclear Regulatory Commission (NRC) classifications refer to these types of waste as low-level wastes. The NRC has outlined three general categories of low-level radioactive waste: Class A, Class B, and Class C. Class B and C wastes involve significant restrictions and licensing in order to handle and dispose of such wastes. However, Class A wastes are much less restrictive to dispose of and present reduced environmental hazards. In recent years, methods have been explored to reduce or remove such contaminants from various areas or surfaces and equipment so that such items or areas may be put back into use and the contaminants may be disposed of safely. These methods have met with varying degrees of success and often present trade-offs between decontamination of the surface or area and the toxicity of the waste product containing the radioactive contaminant.
One method of removing radioactive materials is to physically wash the contaminated area or surface with water and an optional surface-active agent. However, such methods are generally limited to physical separation of contaminants that are not strongly physically or chemically adhered to surfaces or areas. Thus, this method does not work well where the contaminants are chemically bound or strongly physically adhered to a solid surface or structure.
For example, a number of methods have been developed to remove radioactive contaminated scale or rust deposits from metal surfaces that are partially successful. The radioactive substances are removed in a solution that is transported at safe levels for disposal. However the concentrated radioactivity found in scale or rust adhering to surfaces presents increased danger and cost in removal and disposal. Depending on the type of scale or rust deposit either acidic or basic removal treatments may be appropriate. U.S. Pat. Nos. 5,200,117; 5,049,297; and 5,824,159 illustrate typical approaches to removing radioactive substances in these situations.
Another method for removing contaminants from surfaces or areas, which are not necessarily limited to deposited scales, is known generally as acid leaching. In acid leaching methods, a strong acid is used to dissolve radioactive contaminants from the surface into solution. The resulting solution is removed and disposed of leaving a clean, or at least a reduced amount of radioactive contaminants, on the surface. Such acid leaching processes may or may not use chelating agents.
Chelating agents have been the subject of much research in this area and include ligand or binding agents such as oxalate, citrate, gluconate, picolinate, EDTA, hydrazines with carboxylic acids, and hydroxamic acids. Acidic and basic solutions containing a chelating agent are used to dissolve and bind contaminants depending on the characteristics of the surface and the contaminants. When used to remove radioactive substances from contaminated areas, the chelating agent is thought to have the effect of stabilizing certain dissolved radioactive contaminants to keep them in solution. Several of these methods use concentrated carbonate solutions to recover uranium, thorium, radium, technetium, and other actinides.
With several of these methods, a separate ion-exchange process is used to purify the resulting solution to make disposal of the radioactive contaminants easier.
In addition to these challenges, other considerations include providing a decontaminating agent and method which is not excessively corrosive and is easy to prepare and use. Further, the solution containing removed contaminants should preferably be easily disposed of in compliance with state and federal regulations. It would therefore be a significant advancement and contribution to the art to provide a method which is a simple, economic, and effective way of removing substantially all of the radioactive contaminants from various surfaces or areas.
While many methods for removing radioactive or other unwanted contaminants have been developed there remains the need for improved decontamination methods which speed up the decontamination process and remove substantially all of the radioactive contaminants. The present invention relates to the removal of radioactive contaminants from a surface or area using an aqueous solution which includes a wetting agent and an active agent which is a complex substituted keto-amine. The aqueous solution is applied to a radioactively contaminated surface and retained on the surface for a period of time sufficient to allow at least a portion of the radioactive contaminants to migrate into the aqueous solution. The contaminant rich aqueous solution is then removed from the surface for further treatment or disposal. In accordance with the present invention, many Class B and Class C wastes, as defined by the NRC, may be converted to Class A or free release wastes through treatment using the present invention.
In one aspect of the present invention the active agent is a complex substituted keto-amine having the molecular formula C33H45NO2.Cl H.
In a more detailed aspect of the present invention the wetting agent is a member selected from the group consisting of water, lower alcohols, glycols, surfactants, and mixtures thereof.
In another aspect of the present invention, the aqueous solution includes a concentrated acid such as hydrochloric acid, hydrofluoric acid, sulfuric acid, phosphoric acid, sulfurous acid, bromic acid, iodic acid, nitric acid, perchloric acid, oxalic acid, aqua regia, citric acid, sulfamic acid, glycolic acid, ascorbic acid, and mixtures thereof. In a more detailed aspect, the concentration of one or more of the above acids is up to about 10% by weight of the aqueous solution. In a yet more detailed aspect, the concentration of one or more of the above acids is up to about 5% by weight of the aqueous solution. In yet another detailed aspect, the aqueous solution is substantially free of an acid.
In accordance with yet another more detailed aspect of the present invention, the method is used to remove radioactive contaminants, and particularly those found in the actinide and lanthanide series such as thorium, uranium, and plutonium. Exemplary of radioactive contaminants, some of which are in the actinide and lanthanide series, are: Actinium-227, Americium-241, Americium-242, Americium-243, Americium-244, Antimony-124, Antimony-125, Barium-133, Beryllium-7, Bismuth-207, Cadmium-109, Calcium-45, Carbon-14, Cerium-139, Cerium-141, Cerium-144, Cesium-134, Cesium-135, Cesium-137, Chromium-51, Cobalt-56, Cobalt-57, Cobalt-58, Cobalt-60, Copper-64, Copper-67, Curium-242, Curium-243, Curium-244, Curium-245, Curium-246, Curium-247, Curium-248, Curium-249, Europium-152, Europium-154, Europium-155, Gadolinium-153, Germanium-68, Gold-195, Hafnium-181, Hydrogen-3(Tritium), Iodine-125, Iodine-126, Iodine-129, Iodine-131, Iodine-133, Iridium-192, Iron-55, Iron-59, Iron-65, Lead-2.10, Manganese-52, Manganese-54, Manganese-56, Mercury-203, Neptunium-237, Neptunium-239, Nickel-59, Nickel-63, Niobium-94, Niobium-95, Plutonium-236, Plutonium-238, Plutonium-239, Plutonium-240, Plutonium-241, Plutonium-242, Plutonium-243, Plutonium-244, Polonium-210, Potassium-40, Promethium-147, Protactinium-231, Radium-223, Radium-224, Radium-226, Radium-228, Ruthenium-106, Samarium-151, Scandium-46, Selenium-75, Silicon-31, Silver-108 m, Silver-110 m, Sodium-22, Sodium-24, Strontium-85, Strontium-89, Strontium-90, Sulfur-35, Tantalum-182, Technetium-99, Thallium-204, Thorium-natural, Thorium-228, Thorium-230, Thorium-232, Tin-113, Uranium-232, Uranium-233, Uranium-234, Uranium-235, Uranium-236, Uranium-238, Uranium-natural, Uranium-depleted, Yttrium-88, Yttrium-91, Zinc-65, Zinc-69, Zirconium-95, and isotopes and associated decay products of these contaminants.
In accordance with a detailed aspect of the present invention, the method is used to remove transuranic radioactive contaminants.
In accordance with another aspect of the present invention, the method is applied to a solid surface or area as defined above which comprises metal, plastic, glass, concrete, wood, fiberglass, soil, natural or synthetic fabrics, or any other material.
In general, the method comprises applying the aqueous solution, as hereinafter defined, in such a manner as to contact the radioactive contaminant and remove it from the surface or area to which it is associated into the solution. Such application techniques may be by wetting, spraying, wiping, soaking, immersing, and the like. Once applied to a surface it is important that the solution be removed before the solution dries on the surface. Otherwise, the radioactive contaminant would not be removed. Hence, the time the solution is on the surface may be relatively short or long, depending on the wetting time and application process. It may be desirable to sequentially perform more than one application and removal step to adequately remove the radioactive decontaminant from the surface. Additionally, the length of time between the application and removal steps may vary from a few seconds to several minutes depending on the condition of the surface and the amount radioactive contaminant to be removed. Any suitable removal technique, such as a squeegee, wiper blade, vacuum, gravity flow, wringer, centrifuge, and the like may be used to remove the solution from the surface.
In yet another more detailed aspect of the present invention, the application and removal steps may be repeated more than once to remove further portions of the contaminants from the surface. Consecutive treatments may use the same aqueous solution composition or different compositions including linear alcohol alkoxylates, ethoxylated alkyl amines, and mixtures thereof.
Finally, in accordance with another aspect of the present invention the collected aqueous solution containing the removed radioactive contaminant may be treated to neutralize the pH. Collected aqueous solution may be treated by adding sodium hydroxide or any other suitable neutralizing agent to obtain a pH of greater than about 5.5, and preferably about 7 to about 9 to form a waste solution.
Additional features and advantages of the invention will be apparent from the detailed description which follows.
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to exemplary embodiments, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications of the inventive features illustrated herein, and any additional applications of the principles of the invention as illustrated herein, which would occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the invention.
As used herein, xe2x80x9con the surfacexe2x80x9d, xe2x80x9cfrom the surfacexe2x80x9d, xe2x80x9cin the areaxe2x80x9d, xe2x80x9cfrom the areaxe2x80x9d, and the like is intended to cover removal of radioactive particles that are on, near, physically attached to, chemically attached to, embedded in, lodged in the interstices, or otherwise associated with the solid surface or area. As such, the method of the present invention allows for removing or disassociating and then transporting any radioactive particles which are susceptible to contact with the decontamination solution regardless of the physical association or location of such particles in connection with such surface. One surface of particular importance is a porous metal surface, i.e. stainless steel or a surface which has been oxidized, e.g., contains rust, to which radioactive particles have become attached or embedded.
By xe2x80x9csurfacexe2x80x9d or xe2x80x9careaxe2x80x9d is meant the presence of a contaminant on or about a surface or area that may include solid structures, such as trucks, railcars, tanks, pipes, equipment, and the like, particulate, compressible or linear solids such as soils, wires, gauzes, steel wool, fabric and the like. xe2x80x9cAreaxe2x80x9d may also be used to define a location which may be inclusive of liquids such as is found in ponds, tanks, open or enclosed containers, and is inclusive of such containers. In most instances, all contaminants will be associated in, on, attached to, embedded in, or associated with a solid having a surface area. These surfaces can be either exterior or interior surfaces such as in a pipe, tank or other multi-surfaced contaminated body.
As used herein, xe2x80x9clower alcoholxe2x80x9d refers to alcohols having eight of fewer carbons. Such alcohols can be substituted or un-substituted and can be saturated or unsaturated.
As used herein, xe2x80x9clow-levelxe2x80x9d used in conjunction with waste or a surface refers to a radioactive waste which is not used reactor fuel or mill tailings. This term is intended to correspond to the term as used by the NRC and may include any surface which contains radionuclides in measurable quantities. Such low-level waste may be man-made or naturally occurring.
As used herein, xe2x80x9cClass Axe2x80x9d, xe2x80x9cClass Bxe2x80x9d, and xe2x80x9cClass Cxe2x80x9d wastes are intended to refer to low-level waste classifications as defined in 10 C.F.R. xc2xa7 61.55-56 (Jan. 2003). Specifically, classifications are currently based partially on Table 1 and Table 2 below.
Classification is based on whether the waste contains: only radionuclides in Table 1, radionuclides in Table 2 but not in Table 1, radionuclides from both Table 1 and Table 2, or only unlisted radionuclides. Waste containing only radionuclides listed in Table 1 are classified as follows: Class A waste has concentrations which do not exceed 0.1 times the value in Table 1; Class C waste has concentrations which exceed 0.1 times the value in Table 1 but does not exceed that value. Wastes having a mixture of nuclides are classified using a weighted average of the concentration values. Waste containing radionuclides listed in Table 2, and not in Table 1, are classified as follows: Class A waste has concentrations which do not exceed the values in Col. 1; Class B waste has concentrations which do not exceed the values in Col. 2; and Class C waste has concentrations which do not exceed the values in Col. 3. Waste containing a mixture of radionuclides listed in Table 1 and Table 2, are classified as follows: If the radionuclides listed in Table 1 do not exceed 0.1 times the value listed then classification is determined using the radionuclides listed in Table 2; If the radionuclides listed in Table 1 exceed 0.1 times the value listed, then the waste is Class C if the concentration of nuclides listed in Table 2 do not exceed the values in Col. 3. Waste containing only radionuclides which are not listed in either Table 1 or Table 2 the waste are Class A. Although other considerations are also involved such as stability, transportation, and handling requirements the above definitions are sufficient to illustrate the effectiveness of the present invention in reducing concentrations of radionuclides in a variety of surfaces sufficient for classification as Class A low-level waste or as free release.
As used herein, xe2x80x9cfree releasexe2x80x9d refers to surfaces and wastes which are suitable for unregulated release, reuse, and/or disposal. Generally, such free release surfaces will exhibit less than about 1,000 to 5,000 dpm per 100 cm2 depending on the particular radionuclides present.
As used herein, xe2x80x9ctransuranicsxe2x80x9d refers to radionuclides having an atomic number greater than 92. Typically, transuranics are products of artificial or man-made nuclear reactions. Transuranic radionuclides include, without limitation, Neptunium, Plutonium, Americium, Curium, Berkelium, Californium, Einsteinium, Fermium, Mendelevium, Nobelium, Lawrencium, and isotopes thereof.
As used herein, percentages refer to weight percentages unless otherwise specified. Further, one should note that the term xe2x80x9cbetweenxe2x80x9d is used herein to identify a range and without the modifier xe2x80x9caboutxe2x80x9d does not include the limit of the identified range. For example, xe2x80x9cbetween 0.1% and about 3%xe2x80x9d includes values ranging from about 3% by weight, as would be understood in the art down to, but not including 0.1%. Further, a concentration range of xe2x80x9cabout 1% to about 4.5%xe2x80x9d should be interpreted to include not only the explicitly recited concentration limits of 1% to about 4.5%, but also to include individual concentrations such as 2%, 3%, 4%, and sub-ranges such as 1% to 3%, 2% to 4%, etc. The same principle applies to ranges reciting only one numerical value, such as xe2x80x9cless than about 4.5%,xe2x80x9d which should be interpreted to include all of the above-recited values and ranges. Further, such an interpretation should apply regardless of the breadth of the range or the characteristic being described.
The present invention provides a method for removing radioactive contaminants from a contaminated surface or area. As previously noted, a decontamination solution is formed containing a wetting agent and an active agent. The wetting agent is provided to improve the penetration of the solution into the surface of the contaminated material, typically through reduced surface tension. As such, the wetting agent can be any liquid which acts as a carrier and provides an improved penetration of the active agent into the surface of the material as recognized by those skilled in the art. Typical wetting agents can include, without limitation, water, lower alcohols, glycols, surfactants, and mixtures thereof. Consideration in choosing a wetting agent is given to the condition and/or properties of the surface such as oxides, debris, porosity, and surface tension of the wetting agent on the surface, among others. Although various wetting agents may be used in the present invention, lower alcohols such as methanol, ethanol, propanol, isopropanol, butanol, propargyl alcohol, tertiary butyl alcohol, pentanol, hexanol, and mixtures of these alcohols in water provide good wetting properties to the decontamination solution. Other wetting agents include glycols such as, but not limited to, propylene glycol, polypropylene glycol, polyethylene glycol, and ethylene glycol. Any suitable surfactant can be used in the present invention as wetting agents and can include any ionic, non-ionic, cationic, or amphoteric surfactant which is compatible with the active agent as described below. Surfactants suitable for use in the present invention include, but are not limited to, alcohol alkoxylates, ethylene and polyethylene oxides, polyoxyalkenes, aromatic ethoxylates, organic and inorganic salts of polycarboxylated alcohol alkoxylates, linear alcohol sulfates, linear alcohol ethoxysulfates, linear alkylbenzene sulfonates, sulfonates, alkyl sulfates, alcohol alkyloxysulfates, sulfosuccinates, alkanolamides such as nonylphenol alkanolamide, fatty acid esters, ethoxylated triglycerides, ethoxylated alkyl amines, imidosolines, cocamido propyl betaines, sorbitans, and mixtures thereof.
The active agent of the present invention is provided to aid in the removal of radioactive portions of the contaminated material. Active agents of the present invention include complex substituted keto-amines. Additional treatments using second treatment solutions containing various surfactants such as those listed above can be performed either before and/or after treatment using the active agents of the present invention. In one aspect, surfactants such as linear alcohol alkoxylates, ethoxylated alkyl amines, and mixtures of these surfactants can be used. For example, complex substituted keto-amines may be used as the primary active agent, wherein linear alcohol alkoxylates and/or ethoxylated alkyl amines are used in separate subsequent treatments and/or as a pretreatment to further reduce the concentration of radioactive contaminants.
The complex keto-amines of the present invention are rosin amine derivatives having the general formula 
where R is selected from the group consisting of abietyl, hydroabietyl, and dehydroabietyl; wherein Rxe2x80x3 is an alpha ketonyl having fewer than 10 carbon atoms; and wherein Rxe2x80x2 is either H or CH2Rxe2x80x3. The alpha ketonyl group is derived from a ketone used in producing the keto-amine and may include any ketone but is typically a ketone having fewer than ten carbon atoms such as acetone, methyl ethyl ketone, diacetone alcohol, isophorone, mesityl oxide, pentane dione, acetonyl acetone, cyclopentanone, cyclohexanone, and acetophenone. The process for manufacture of these types of keto-amines is described more fully in U.S. Pat. No. 2,758,970, hereby incorporated by reference. One such complex substituted keto-amine has the molecular formula C33H45NO2.Cl H and may also be identified by the CA Index chemical name 2-Butanone, 4-[[[(1R,4aS,10aR)-1,2,3,4,4a,9,10,10a-octahydro-1,4a-dimethyl-7-(1-methylethyl)-1-phenanthrenyl]methyl](3-oxo-3-phenylpropyl)amino]-, hydrochloride (9Cl). Generally, complex substituted keto-amines will constitute less than about 10% and most often between about 1% and about 5% or between about 0.1% and about 2% by weight of the total decontamination solution. Decontamination solutions containing these active agents have shown good results on a wide variety of surfaces.
The linear alcohol alkoxylates of the present invention are ethoxylated and propoxylated alcohols having from six to fifteen carbons. Such linear alcohols are known by the CA Index name alkoxy, C6-10 or C 12-15, ethoxylated propoxylated alcohols. The alkoxylates may be present in the second treatment solution at levels less than about 5% by weight of the total solution. Treatment solutions containing between about 0.05% and about 5% have shown good results. Typically, these surfactants require lower concentrations in this range and concentrations below about 1% work well for most surfaces.
The ethoxylated alkyl amines of the present invention are ethoxylated alkyl amines wherein the alkyl group is a long-chain alkyl having greater than seven carbon atoms. Such amines may be derivatives of a variety of oils such as coconut oil (ethoxylated coco alkyl amine), palm kernel oil, and other oils. Ethoxylated amines used in the present invention may constitute less than about 5% by weight of the total treatment solution. Concentrations of ethoxylated amines may also range from about 1% to about 4% by weight of the total treatment solution. This surfactant has shown particularly good results on concrete and stainless steel surfaces.
The aqueous solution of the present invention can also include a concentrated acid. Typically, surfaces having a greater amount of scale, rust, or other layers of debris covering the contaminated area will require the addition of a concentrated acid. Surfaces which are substantially free of such debris often do not require the addition of an acid to the aqueous solution of the present invention or require only very dilute acid concentrations therein. If used, the concentrated acid may be a strong acid such as hydrochloric acid, hydrofluoric acid, sulfuric acid, phosphoric acid, sulfurous acid, bromic acid, iodic acid, nitric acid, perchloric acid, oxalic acid, aqua regia and mixtures of such strong acids. Other acids such as citric acid, sulfamic acid, glycolic acid, and ascorbic acid may also be used in the method of the present invention. Hydrochloric acid exhibits particularly good results and may be used in a concentrated aqueous solution of about 32% to 38% hydrochloric acid. The currently used concentration for hydrochloric acid is 37% which is then added to the aqueous solution in varying amounts. Concentrations of between about 1% and about 10% of hydrochloric acid in the aqueous solution have shown excellent results on some surfaces. When a concentrated acid is used the concentration may be sufficient to provide a pH of about 3 or lower and preferably about 1.5 or below and more preferably below about 1.0. Frequently, less acidic aqueous solutions will also work for a variety of surfaces. As such, the concentrated acid may comprise up to about 10% of the aqueous solution. In a more detailed aspect, the concentrated acid may comprise up to about 5% of the aqueous solution. These concentrated acids may be added to the decontamination solution alone or in combination with other acids. Additionally, some surfaces can be treated with the aqueous solution of the present invention which is substantially free of an acid.
Other additives or components may be added to the decontamination solution in order to enhance various properties of the solution. Such additives may include catalysts such as copper chloride, nickel chloride, iron chloride; basic components such as ammonium bifluoride or diammonium citrate; or a variety of other additives such as surfactants or corrosion inhibitors.
Once the aqueous decontamination solution is prepared according the present invention the contaminated surface may be cleaned and prepared to remove any dirt, oil, dust, or other debris prior to applying the solution to the surface. If the surface contains organic materials, such as oils or certain surfactants, it may be preferable to clean the surface with other appropriate materials, solvents, cleaning agents such as acetone, methylethyl ketone, steam, strong surfactants, or other agents known to those skilled in the art. The use of water and/or steam is acceptable; however the use of some surfactants was shown to reduce the effectiveness of the present invention.
As noted above, the contaminated surface may be any solid surface which exhibits undesirable levels of radioactive particles such as thorium, uranium, plutonium, transuranics, other elements from the actinide and lanthanide series of the periodic table as well as other radioactive substance as previously listed. As also previously noted, such surfaces may include, but are not limited to, metals, plastics, glass, wood, concrete, fiberglass, fabrics, and soil. Transportation equipment such as railcars, trucks, ships, forklifts, containers, pumps, covers, and pipes often become radioactively contaminated during transport of waste materials and are particularly suited to being treated according to the present invention. Stationary surfaces such as buildings and process equipment are also often contaminated with radioactive particles. Other materials include polymeric materials, polyethylenes, rubbers, nuclear reactor equipment, nuclear reactor pipe, scrap metal, boilers, glove boxes, spent nuclear fuel rods, and any other equipment, containers or parts which are used in handling, using, processing and transporting radioactive materials. It is to be understood that the above recited lists of various specific surfaces are intended to merely illustrate some of the types of surfaces which may be used in connection with the present invention, and are not intended to limit the scope thereof. Frequently, prior to treatment, these surfaces are classified as Class B, Class C, or high-level radioactive wastes. These classes of wastes are accompanied by significant additional disposal, transportation, and handling restrictions. The radionuclide concentration of many of these surfaces may be reduced using the present invention sufficient to be classified as Class A wastes or even as free release, thus allowing for more economical disposal and reduced environmental hazard.
In accordance with the present invention, the decontamination solution is then applied to the contaminated surface. The aqueous decontamination solution may be applied using any conventional method such as spraying, immersing, brushing, wetting, providing a continuous flow of fresh solution (as through a pipe or over a surface), and any other method which produces direct contact of the decontamination solution with the contaminated surface. Although, a variety of application devices may be used as is known in the art, spraying and wetting have produced satisfactory results. Accordingly, the decontamination solution may be placed in a device which is capable of producing a spray or wetting action and is designed for highly acidic contents. Such spraying devices include without limitation hand spray bottles, lightweight sprayers, and industrial spraying machines (either manual or automated). The wetting devices required for the present invention allow for a highly portable process.
In an additional aspect of the present invention, ultrasonic energy may be introduced at the surface of the contaminated article. A variety of methods may be used to apply the ultrasonic energy such as ultrasonic brushes, actuators or the like. The ultrasonic energy may be at a frequency above about 20 kHz and in one aspect is above about 50 kHz. In one embodiment, in addition to spraying, an ultrasonic brush may be used on the surface which accelerates removal and lessens the treatment time. Such an ultrasonic brush has significantly decreased treatment times on vertical surfaces where the decontamination solution merely wets the surface. Various tests have shown a decrease in treatment time of over 50% and often over about 80%. Typical treatments using ultrasonic energy decrease treatment time to less than about 3 minutes to achieve the same results as obtained without the use of an ultrasonic energy source in treatments of up to about 20 minutes. Although not fully understood, it is thought that the ultrasonic vibrations propagate through the solution at the surface and improves the ability of the wetting agent to penetrate into the surface at an increased rate over that without the ultrasonic treatment. Accordingly, ultrasonic waves directed toward the contaminated surface having a decontamination solution thereon should also increase the rate of contaminant removal according to the present invention.
In still another aspect of the present invention, infrasonic energy may be applied during treatment using the aqueous solutions of the present invention. Such infrasonic energy further improves the rate and degree of removal of radioactive contaminants from the surface. Without being bound to any particular theory, it is thought that the infrasonic energy increases the removal of radionuclides from positions further into the interior of the surface than treatments without such energy. Typical infrasonic energy frequencies range from about 1 Hz up to and not including 20 Hz and in one aspect are from about 10 Hz up to but not including 20 Hz.
In yet another aspect of the present invention, sonic energy can be applied during treatment using the decontamination solutions of the present invention. Typical sonic energy frequencies range from 20 Hz to 20 KHz.
In one aspect of the present invention, treatment can include a combination of ultrasonic and infrasonic energy, ultrasonic and sonic energy, or infrasonic and sonic energy. Application of such combinations of energy can be simultaneous, consecutive or alternating. Further, results are improved if the ultrasonic, infrasonic and/or sonic energy is applied at the surface or immediately adjacent thereto. Although precise effective distances will depend on the amplitude of the energy, typical effective distances are less than about ten inches and in one aspect are less than about one inch. In one embodiment, the energy is applied directly at the surface.
The temperature of the decontamination solution may be whatever is functional and is preferably ambient temperature of less than about 45xc2x0 C. At temperatures above about 50xc2x0 C. the decontamination solution vaporizes and does not decontaminate the surface. In other words, although some moderate heating can improve performance, i.e. up to about 45xc2x0 C., the aqueous solution usually does not require heating at temperatures above about 1 to 5xc2x0 C.
Application rates and amounts are best determined empirically and are based on the amount or concentration of radioactivity on the contaminated surface, the depth of scale or rust containing the contamination on the surface, the surface area to be treated, whether sequential application and removal is desired, and the like. What is required is that a functional area or surface is treated with the aqueous solution and allowed to remain for a time sufficient to remove the radioactive materials that are contacted followed by removal of the contaminant containing solution. The area treated is limited to that which can adequately be treated and the solution removed by the operator. Generally speaking, the solution will remain on the surface for ten minutes or less and will preferably be on the surface for five minutes or less. However, for some operations the solution may remain for longer periods sufficient to translocate the radioactive particles from the surface. It may be preferable to treat the surface with a succession of treatments where the solution is applied and removed followed by sequential treatments of application and removal until the desired result is obtained. It is not the time or amount that is critical as these parameters may be empirically determined. For example, the treatment time will vary considerably depending on the type of surface treated, but is generally under ten minutes. Typically, surfaces such as steel, iron and other metal surfaces will require shorter treatment times than more porous surfaces such as concrete, wood, plastic, and fiberglass.
In a more detailed aspect of the present invention, sequential treatments are made using decontamination solutions having different compositions. Some contaminated surfaces may benefit from such a consecutive treatment process. For example, a first treatment of the surface may be made by applying a complex keto-amine decontamination solution and then removing the solution containing a portion of the radioactive contaminants as described above. A second treatment may then be made using another solution such as a linear alcohol alkoxylate solution or a solution containing a concentrated acid. Various combinations of consecutive treatments may be made based on routine experimentation by those skilled in the art. Experimentation has shown that repeated treatment using the same solution is often not as effective for reducing contamination as consecutive treatments using different solutions.
One important benefit of this invention is the speed and efficiency of the decontamination process. After treating the surface with the aqueous solution the solution containing the radioactive contaminants may be removed using conventional methods such as gravity flow, vacuuming, using a wiper blade or squeegee, rinsing or any other appropriate means and collected in a separate collection container. As previously mentioned, application times of less than about 5 minutes such as about 1 to 3 minutes have produced excellent decontamination results. The application and removal process may also be repeated and has the effect of further decreasing the concentration of radionuclides. Additionally, the method of the present invention may be performed using highly portable equipment including an aqueous solution container, an application device, a contaminated solution receiving container, and an optional collection device.
In one aspect of the present invention, prior to treatment, the surface is a low-level radioactive surface. In a more detailed aspect of the present invention, the low-level radioactive surface prior to treatment has a radioactivity concentration of between about 0.1 and about 1.0 curie per cubic foot. In yet a more detailed aspect of the present invention, the low-level radioactive surface prior to treatment has a radioactivity concentration of between about 1.0 and about 7.0 curies per cubic foot. These radioactivity concentrations are intended to generally correspond to Class A, Class B, and Class C low-level wastes as defined by the NRC and 10 C.F.R. xc2xa7 61.55-56. Typically, surfaces having radioactivity concentrations of less than about 0.1 curie per cubic foot are freely releasable into the environment after about 100 years. likewise, surfaces having radioactivity concentrations of between about 0.1 and about 1.0 curie per cubic foot are generally freely releasable into the environment after about 300 years. Surfaces having radioactivity concentrations of between about 1.0 and about 7.0 curies per cubic foot are typically freely releasable into the environment after about 500 years. Frequently, treatment using the method of the present invention will immediately result in a free release material and is not subject to NRC restrictions regarding disposal, handling, and transportation. In one aspect, subsequent to treatment in accordance with the present invention and removal of the aqueous solution therefrom, the surface can have a concentration of radionuclides of less than about 0.1 curie per cubic foot. In another aspect, subsequent to treatment, Class C or Class B surfaces can be reduced to Class B, Class A, or free release wastes. In yet another aspect, the surface is a high-level radioactive waste having a radioactivity of about 7.0 curies per cubic foot prior to applying the aqueous solution thereon. After treatment in accordance with the present invention, such surfaces can be reduced to Class C, Class B, Class A, or even in some cases free release.
After the decontamination solution is removed from the surface further treatment of the surface may be desirable. The resulting surface is often exposed bare metal and as such may oxidize. The decontamination solution of the present invention does impart some degree of corrosion resistance to treated surfaces. If necessary, treatment with corrosion inhibitors such as phosphoric acid and other known products may improve the long-term corrosion resistance of treated metal surfaces.
In another more detailed aspect of the present invention, the spent solution in the collection container containing the removed radioactive materials is neutralized to a pH of 5.5 to about 9.0 and preferably about 6 to about 8 by means of aqueous sodium or potassium hydroxides or other alkaline neutralizing agents. In order to increase efficiency, the monitoring and addition of alkaline solution may be accomplished using automated equipment, although the process could be done manually. An alkaline solution, such as sodium hydroxide or potassium hydroxide is added to the collected solution which contains radioactive contaminants to reach a pH of greater than 5.5. A collected solution having a pH in the range of about 6.5 to 9 makes storage and disposal of the radioactive solution easier and safer.
Conventional means may be used to remove the neutralized contaminated solution to a suitable disposal site in accordance with established regulatory procedures. The neutralized contaminated solution resulting from use of the present invention exhibits very low disintegrations per minute (dpm) values and may therefore be readily disposed of according to existing state and federal regulations.
The neutralized contaminated solution may be disposed of in a variety of ways known to those skilled in the art. The contaminated solution may be centrifuged to remove a portion of the radionuclides, however many radionuclides will remain in solution. Various flocculating agents, precipitating methods, or ion-exchange processes may also be used and are known to those skilled in the art. Frequently, the contaminated solution may also be solidified using various methods such as solidifying polymers, porous adsorbents, cementation, vitrification, and the like. The solidified solution may then be disposed of according to existing state and federal regulations.